Bipolar junction transistors are non-linear transconductors and for this reason their use in linear amplifiers requires the use of special techniques such as negative feedback. Without feedback, a simple differential pair as shown in FIG. 1 has a very non-linear gain as illustrated graphically in FIG. 2. Negative feedback can be applied to a single stage amplifier in shunt mode, as in a transimpedance amplifier, or in serial mode, as in the application of emitter degeneration, or, sometimes in both shunt and serial feedback modes simultaneously. Such application of feedback generally requires the use of resistors as linear circuit elements to control the amplifier gain. In low noise amplifier applications, the use of resistors can be a disadvantage since they are a well known source of thermal noise and this impairs the amplifier noise figure. A further disadvantage of series negative feedback is that the amount of feedback depends upon the transistor bias level and in the case of a variable transconductance amplifier, the amount of feedback varies also and consequently so does the amplifier linearity. As a result, series negative feedback can be inappropriate for variable transconductance amplifiers.